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Structural material AA-7075-T6, an aluminium-based alloy, was subjected to thermal exposure for 60 min in the temperature range 100–300 °C with an interval of 20 °C. Harris analysis of the XRD patterns of specimens showed that the un-exposed AA-7075-T6 material was texture free, but upon thermal exposure, it developed texture. The crystallite size and lattice strain of the specimens were evaluated by Williamson-Hall analysis of the XRD patterns. Thermal exposure in the temperature range 100‒200 °C had no noticeable effect on the surface hardness. However, it decreased rapidly with the increase in temperature from 200 to 300 °C. This behaviour was accounted for in terms of dislocation glide by Orowan mechanism in an atmosphere of semi-coherent ή precipitates (MgZn2) in the main matrix. Breakdown of Hall–Petch relation established that crystallite boundaries do not make any significant contribution to the surface hardness, but the resistance to glide dislocations is offered by the semi-coherent ή precipitates (MgZn2) present in the matrix. [ABSTRACT FROM AUTHOR]

Zinc single crystal specimens were irradiated with pulsed Nd:YAG laser in vacuum. Keeping the number of laser shots constant (10 shots), laser energy was varied from 50 to 150 mJ, whereas the corresponding laser fluence was 97 to 292 J cm−2, respectively. Using optical microscope, the dimensions (area and perimeter) of laser ablated region on the surface of each specimen were measured. Both parameters increased, in general, on increasing laser pulse energy. Examination of surface morphology by scanning electron microscope revealed formation of pores, grooves, cracks, bubbles, micron-size rods, ripples, ridges, cavities, microcones, and solid flakes, etc. Surface roughness had no systematic dependence on the laser pulse energy. Structural parameters, i.e., texture coefficient, lattice strain, and crystallite size, were determined by means of Harris analysis as well as Williamson–Hall analysis of the XRD patterns of specimens. The variation of lattice strain and crystallite size with laser fluence or laser pulse energy was alike. Surface hardness decreased on increasing laser fluence, and followed classical Hall–Petch relation. [ABSTRACT FROM AUTHOR]

A theoretical model is developed to describe the influence of recovery and recrystallization on the macroelastic limit, the yield strength, and the grain-boundary hardening coefficient of the submicrocrystalline (SMC) metals fabricated by severe plastic deformation. The anomalous hardening and the increase in the grain-boundary hardening coefficient upon annealing of the SMC metals are shown to be related to defect accumulation in migrating grain boundaries in them. Equations are derived to relate the Hall-Petch relation parameters to the grain-boundary migration velocity, the nonequilibrium state of grain boundaries, the lattice dislocation density, and the annealing temperature and time. The results of the numerical calculations performed using the developed model are compared with the experimental results obtained in part I of this work. [ABSTRACT FROM AUTHOR]

A model is developed to calculate the Hall-Petch relation parameters for the submicrocrystalline (SMC) metals fabricated by severe plastic deformation (SPD) methods. The model is based on the assumption that the flow stress in SMC metals includes both conventional contributions (caused by lattice dislocations, impurity atoms, etc.) and a contribution related to the long-range internal stress fields created by the SPD-induced defects distributed over grain boundaries. Equations are derived to calculate the Hall-Petch relation parameters as functions of the strain and the strain rate. The results calculated by the derived equations agree well with the experimental data. The low resistance of grain boundaries to the motion of grain boundaries in SMC materials (see part I of this work) is found to be related to a violation of the Hall-Petch relation in SMC metals. [ABSTRACT FROM AUTHOR]

Physical modeling of deformation of a hardening composite sample with a filler made of quartz sand with different grain sizes has established a relation between the acoustic emission parameters in the heated geomaterial, its grain size and strength. Anomalous acoustic emission has been revealed within definite heating temperature ranges, correlating the geomaterial strength in the first case and with the geomaterial grain size in the second case. The resultant experimental relation between the strength and grain size of agrees with the Hall-Petch relation. [ABSTRACT FROM AUTHOR]

It is shown that, in the case where the grains in polycrystalline materials are refined to nanocrystalline sizes, there are two critical sizes the attainment of which leads to changes in the mechanism of hardening. A generalized equation for the description of the dependence of the yield strength on the grain size is deduced for a broad range of parameters with regard for the changes in the character of this dependence observed as the indicated critical grain sizes are attained. [ABSTRACT FROM AUTHOR]

The paper considers the influence of size effects on dislocation structure and second-phase particles. Particular attention is given to scalar dislocation density, geometrically necessary dislocation density and parameters of particles formed at grain boundaries. It is found that there exist three critical grain sizes in the range of which the mechanisms of deformation and hardening of polycrystals are changed. Special emphasis is placed on stabilization of the submicropolycrystal grain structure by second-phase particles present at the grain boundaries. [Copyright &y& Elsevier]